In a paper presented at the spring meeting of ACS Rubber Division held on May 8-11, 1984 in Indianapolis, Ind., Dr. K. H. Nordsiek discussed model studies for the development of an ideal tire tread rubber. The postulated ideal rubber for tire tread is not capable of description by a characteristic glass transition temperature, T.sub.g, which is considered a useful physical criterion for determining the characteristics of amorphous rubbers. Instead, the ideal rubber represents the sum of a large number of different block structures having varying T.sub.g values.
Batch polymerization of 1,3-butadiene monomers with styrene monomers in the presence of an anionic initiator yields a block copolymer having a slight taper due to differences in the reactivity of the monomers. However, there are still two sharp glass transition temperatures associated with formation of both a mostly polybutadiene block and a mostly polystyrene block.
Batch polymerization of 1,3-butadiene monomers with styrene monomers in the presence of an anionic initiator and a modifier also leads to a taper in the 1,2-microstructure of the butadiene segments when the polymerization temperature is permitted to rise adiabatically. However, the styrene distribution is fairly uniform and the butadiene microstructure taper is dependent on many factors including: the total change in temperature, .DELTA.T; the initial and maximum reaction temperatures; and the degree of polymerization conducted at each temperature. A distinct T.sub.g is present for these polymers. It is therefore desirable to precisely control tapering and prepare a postulated ideal rubber for use as tire tread in a continuous process.
It is therefore an object of the present invention to provide a continuous process for the production of a styrene-butadiene type copolymer having a continuously tapered structure and possessing no specific T.sub.g values.